The invention relates to active acoustic attenuation systems, and provides a system for attenuating and spectrally shaping an acoustic wave.
The invention arose during continuing development efforts relating to the subject matter shown and described in U.S. Pat. Nos. 4,677,676, 4,677,677, 4,736,431, 4,815,139, 4,837,834, 4,987,598, 5,022,082, and 5,033,082, incorporated herein by reference.
Active attenuation involves injecting a canceling acoustic wave to destructively interfere with and cancel an input acoustic wave. In an active acoustic attenuation system, the output acoustic wave is sensed with an error transducer such as a microphone which supplies an error signal to a control model which in turn supplies a correction signal to a canceling transducer such as a loudspeaker which injects an acoustic wave to destructively interfere with and cancel the input acoustic wave. The acoustic system is modeled with an adaptive filter model.
In the invention of the noted parent application, the error signal from the error transducer, e.g. error microphone, is specified to correspondingly specify the output acoustic wave. The error signal is specified by summing the error signal with a desired signal to provide an error signal to the error input of the system model such that the model outputs the correction signal to the output transducer, e.g. speaker, to introduce the canceling acoustic wave such that the desired signal is present in the output acoustic wave. This provides a desired sound rather than complete cancellation.
The present invention provides further improvements for spectrally shaping the acoustic wave.
In one aspect of the present invention, the system includes a phase lock loop phase locked to the input acoustic wave, and generates a desired signal in given phase relation therewith. The error signal from the error transducer is summed with the desired signal from the phase lock loop, and the resultant sum is supplied to the error input of the model such that the model outputs the correction signal to the output transducer to introduce the canceling and shaping acoustic wave.
In another aspect, a first summer sums the error signal from the error transducer with a desired signal and supplies the resultant sum to the error input of the model, and a second summer sums the correction signal from the model with the desired signal and supplies the resultant sum to the output transducer.
In a further aspect, another summer sums the error signal from the error transducer with the correction signal supplied through a copy of a model of the output transducer and error path and supplies the resultant sum to the first summer.
In another aspect, the desired signal is supplied through a copy of a model of the output transducer and error path to the first summer.
In a further aspect, the desired signal is supplied through an inverse of a copy of a model of the output transducer and error path to the second summer.
In another aspect, a first summer sums the error signal from the error transducer with a desired signal and supplies the resultant sum to the error input of the model, and a second summer sums the input signal to the model with the desired signal and supplies the resultant sum to the model input.